Calcination of hydrated alumina.



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ALFRED RANGOD Pl JClllNltY, UF

(JOMPAGNTE DES PltUl'JUlTS MARGUE, Uh LYON, ill-LANCE.

Specification of Letters Patent.

Patented Jan. 80, 1906.

Application filed April 8, 1905. Serial No. 253,580. I

To rtZZ whom it may concerrt' Be it..known that 1, human Rnncon PE-CHINEY, residingat Salindres, Department of Gard, in the Republic ofFrance, have invent-- edlmprovements in the Ualcination of HydratedAlumina, of which the following is a specification.

1 For certain uses alumina requires to be dehydrated by calcination ascompletely as possible, notably when it is to serve for the manu factureof aluminium by the electrometallurgical rocesses at present in use. Toattain comp ete dehydration, a very high tempera ture is required at thefinal period of the cal cination. Moreover, if the material does notremain exposed during a suflicient period oi time to this very hightemperature it has after it cools down again an inconvenient aptitude ofpartially rehydrating itself under the sole influence of atmosphericmoisture. These difficulties which the complete dehydration of aluminaoffers are considerably lessened When there is incorporated with thealumina to'be calcined a small predetermined quantity of a l'luorid. Thepresence of the fluorin roduces in a very decided manner the iol owingadvantages or results: First, the final temperature of the calcinationmay be considerably less than heretofore usual Without interference Withthe perfect calcin ation; secend, the exposure of the material to thehigh final temperature does not need to be prolongated "for renderingtheproduct after calcination not liable to become rehydrated by ex posureto the atmosphere; third, finally at about 1,-ZOO centigrade thematerial in the furnace becomes suddenly agglomerated in coherentm'asses. v

The improvements which form the object of the present invention arebased upon the preceding observations. According to this invention aconvenient fluorid is incorporated with the alumina which itis.;.desired to calcine. This incorporation may be simply done bysprinkling and mixing the product to be calcined with dilutehydrofluoric acid or with a dilute solution of aluminium fluorid.

The proportion of fluorin necessary is very small. or example, 0.25 ofone part oi fluorin to one hundred parts of anhydrous I alumina yieldsquite appreciable results. its

' augmentation up to one part of fluorin to one htnrdred parts atanhydrous alumina is,

however, to be recommended, as this gives the best results both as tocostand the perfeet-ion oi the calcination. tity (one per cent.) ol"lluorin the agglomeration of the final anhydrous alumina attains verynearly'the maximum possible density. Hydrofluoric acid and fluorid ofaluminium should be employed in preference to all other fluorids, ashydrofluoric acidand fiuorid of aluminium cannot introduce into thealumina any irn urity other than traces of fluorin, which, oWever, isvolatilized during the calcination in a manner sometimes so completethat it exceedingly diflicult to discover traces in the calcinedalumina.

To carry out the process in practice, a solu tion of fluorid ofaluminium of, say, from 12 to 14 Baume may be employed and this solutionmixed with the hydrate of alumina to be calcined, the one being added tothe other in quantities such that the mixture may contain very nearlyone part of fluorin to one hundred parts of anhydrous alumina. Theseindications are only given by Way of example, and it is to be understoodthat it is not desired to restrict or limit the carrying out of the invention. After mixture the material is calcincd in an appropriatefurnace. The agglomerated lumps or pieces are after cooling reduced bycrushing or grinding, if required, to

for which the anhydrous alumina is intended. When it is proposed toobtain the anhydrous alumina agglon'ierated in the form of bricks,slabs, or the like capable of being used, say, for furnace-linings, theyare very refrae tory, the calcination of the hydrated alumina admixedwith a fluorid should be carried out by preference in appropriate molds.

What I claim is r 1. The improved process of calculating hydratedalumina, according to which such hy drated alumina is calcined in thepresence of a fluorid at a temperature of 1,300 centigrade, orthereabout, substantially as set forth for the purpose specified.

The improved process of calcinin hydrated alumina, accordin to whichsuch by dratecl alumina is calcined in the presence of the calcinationis effected, substantially as set forth for thepurpose specified. 35.The improved process of calcining hythe state of division which bestsuits the use a fiuorid volatile at the temperature to which dratcdalumina, according to which such hydrated alumina is calcined in thepresence of liuorid of aluminium, substantially as set forth for thepurpose specified.

4. The improved process of calcininghydrated alumina, according to whichsuch hydrated alumina is calcined in the presence of a fiuorid, themixture containing approximately one part of fiuorin' to one hundredparts of anhydrous alumina, substantially as set forth for the purposespecified.

5. In the oalcination of hydrated alumina,

mixing a solution of fluorid of aluminium with the hydrate of alumina tobe calcined, so that the mixture contains sayone part of fluorin to onehundred parts of anhydrous alumina. In testimony whereof I have signedmy name to this specification in the presence of two subscribingwitnesses.

ALFRED RANGOD PEGHINEY.

Witnesses:

HENRI CARTIER, AUGUSTUS JEANs.

